Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session P14: Topological Materials - Theory and computationFocus
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Sponsoring Units: DMP Chair: Haizhou Lu, Southern University of Science and Technology, China Room: LACC 304B |
Wednesday, March 7, 2018 2:30PM - 3:06PM |
P14.00001: Where are we in the jungle of topological materials? Invited Speaker: Arun Bansil It is just about a decade ago that the quantum-spin-Hall insulator state was observed in HgTe/CdTe quantum wells, followed by the realization of the 3D topological insulator state in BiSb alloys. These discoveries launched an intense worldwide effort on topological states protected by time-reversal symmetry constraints and the associated exotic phenomena, leading to the Nobel Prize in physics in 2016. Last few years have seen a great expansion of the field, which now encompasses protected states of quantum matter that arise through combinations of time-reversal, crystalline and particle-hole symmetries. Despite these advances, the field is still in its infancy and many more surprises can be expected involving 2D and 3D topological materials and their interfaces and heterostructures with magnetic, non-magnetic and superconducting materials. I will highlight some of the progress that has been made, including our own recent work [1-6], and comment on the outstanding open questions. |
Wednesday, March 7, 2018 3:06PM - 3:18PM |
P14.00002: Symmetry-Based Indicators of Band Topology I: Formalism Hoi Chun Po, Haruki Watanabe, Ashvin Vishwanath We develop an efficient theory to answer one of the oldest questions in band theory, namely, what are the possible symmetry-respecting ways to connect energy bands across the Brillouin zone? We find solutions for all 1,651 magnetic space groups in 3D, from which we extract fundamental physical quantities, like the minimal number of electrons required to form a band insulator, and how nontrivial band topology may be reflected in the symmetry eigenvalues. |
Wednesday, March 7, 2018 3:18PM - 3:30PM |
P14.00003: Symmetry-Based Indicators of Band Topology II: Applications HARUKI WATANABE, Hoi Chun Po, Ashvin Vishwanath How do the symmetry representation of band structures relate to band topology? For space groups with inversion symmetry, the Fu-Kane formula determines the strong/weak index of a band structure based on the parity eigenvalues of the occupied bands. We generalize the relation between symmetry representation and band topology to all 230 space groups and further to all 1651 magnetic space groups. Examples of nontrivial band topology indicated by symmetry representation include topological insulators, (mirror) Chern insulators, and even Weyl/nodal line semimetals. In particular, two copies of a strong topological insulator turns out to be still nontrivial in the presence of inversion symmetry. In this talk, we will discuss these interesting examples in detail. |
Wednesday, March 7, 2018 3:30PM - 3:42PM |
P14.00004: New topological phases and new materials using Topological Quantum Chemistry Maia Vergniory, Barry Bradlyn, Jennifer Cano, Zhijun Wang, Luis Elcoro, Mois Aroyo, Claudia Felser, Andrei Bernevig During this talk, I will examine topological metals and insulators stabilized by any of the |
Wednesday, March 7, 2018 3:42PM - 3:54PM |
P14.00005: Predicting and Understanding Quantum Spin Hall Insulators with the Help of Compressed Sensing/SISSO. Carlos Mera Acosta, Runhai Ouyang, Adalberto Fazzio, Matthias Scheffler, Luca Ghiringhelli, Christian Carbogno Quantum Spin Hall insulators (QSHIs), i.e., two-dimensional insulators with conducting edge states protected by time-reversal symmetry, have attracted considerable scientific interest in recent years. In this work, we perform first-principles calculations to compute the Z2-invariant for 220 functionalized honeycomb-lattice materials. Using the recently developed sure independence screening and sparsifying operator (SISSO) method [1], we derive a "map of materials", in which metals, trivial insulators, and QSHIs are spatially separated. The axes of this map are defined by physically meaningful descriptors, i.e., non-linear functions that only depend on the properties of the material’s constituent free atoms. First, this yields fundamental insights into the mechanisms driving topological transitions. Second, we are able to predict the topological character of materials that are not part of the originally investigated set just from their position on the map (predictive power greater than 95%). By this means, we are able to predict 89 yet unknown QSHIs. |
Wednesday, March 7, 2018 3:54PM - 4:06PM |
P14.00006: Topological Markers in Disordered, Amorphous, and Quasicrystalline Materials Using KPM. Daniel Varjas, Pablo Perez-Piskunow, Anton Akhmerov We implement the kernel polynomial method (KPM) to investigate the topological properties of two and three dimensional materials without translation invariance. By efficiently calculating topological markers, such as the local Chern number and local magnetoelectric coupling, we assess the topological character of disordered model systems. Furthermore, by calculating surface density of states, the ARPES spectra can be simulated for nonperiodic samples. We use these methods to search for material candidates of amorphous and quasicrystalline topological insulators. |
Wednesday, March 7, 2018 4:06PM - 4:18PM |
P14.00007: Topological Electrides and Quantized Zak Phase Motoaki Hirayama, Satoru Matsuishi, Hideo Hosono, Shuichi Murakami Recent studies on the topology of the band structure in the k-space have revealed possibilities of various topological insulators and topological semimetals. Here, the topological semimetals include the Dirac semimetals, the Weyl semimetals [1,2], and the nodal-line semimetals [1,3]. In my presentation, we show that electrides are suitable for achieving various topological insulating and topological semimetal phases. We present an example of an electride showing the topologically insulating phase characterized by the \pi Zak phase. This can be considered as a limit of the topological nodal-line semimetal [3] like calcium, where the Zak phase is either \pi or 0 depending on the momentum regions divided by the nodal lines. This \pi Zak phase appears as a surface polarization charge, and we propose that this surface charge is useful for carrier doping by using the electride. We also talk about the materials having other topological phases such as a nodal-line semimetal. [1] S. Murakami, M. Hirayama, R. Okugawa, and T. Miyake, Sci. Adv. 3 e1602680 (2017). [2] M. Hirayama, R. Okugawa, S. Ishibashi, S. Murakami, and T. Miyake, Phys. Rev. Lett. 114, 206401 (2015). [3] M. Hirayama, R. Okugawa, T. Miyake, and S. Murakami, Nat. Commun. 8, 14022 (2017). |
Wednesday, March 7, 2018 4:18PM - 4:30PM |
P14.00008: Chiral Topological Excitons in a Chern Band Insulator Ke Chen, Ryuichi Shindou A family of semiconductors called Chern band insulators are shown to host exciton bands with nonzero topological Chern integers and chiral exciton edge modes. Using a prototypical two-band Chern insulator model, we calculate a linear response function among the density and pseudospin degrees of freedom to obtain the exciton bands and their Chern integers. Eigenvalues of the matrix-formed response function have a well-defined pole below the electron-hole continuum, which describes an energy-momentum dispersion for exciton excitations in the Chern insulator. We define a topological Chern integer for exciton bands from the corresponding eigenvectors. The lowest exciton band acquires the Chern integers such as ±1 and ±2 in the electronic Chern insulator phase. The nontrivial topology can be experimentally observed both by a nonlocal optoelectronic response of exciton edge modes and by a phase shift in the cross-correlation response due to the bulk mode. Our result suggests that magnetically doped HgTe, InAs/GaSb quantum wells, and (Bi,Sb)2Te3 thin films are promising candidates for a platform of topological excitonics. |
Wednesday, March 7, 2018 4:30PM - 4:42PM |
P14.00009: The New Phases due to Symmetry Protected Piecewise Berry Phases Xuele Liu, Girish Agarwal Finding new phase of matter is a fundamental task in physics. Generally, various phases or states of matter (for instance solid/liquid/gas phases) have different symmetries, the phase transitions among them can be explained by Landau’s symmetry breaking theory. The topological phases discovered in recent years show that different phases may have the same symmetry. The different topological |
Wednesday, March 7, 2018 4:42PM - 4:54PM |
P14.00010: Antiferromagnetic Chern insulators in non-centrosymmetric systems Kun Jiang, Sen Zhou, Xi Dai, Ziqiang Wang A new class of topological antiferromagnetic (AF) Chern insulators driven by electronic interactions can emerge from two-dimensional systems without inversion symmetry. Despite the absence of a net magnetization, |
Wednesday, March 7, 2018 4:54PM - 5:06PM |
P14.00011: Majorana Stripe Order at the Surface of a 3D topological Insulator Yoshitomo Kamiya, Akira Furusaki, Jeffrey Teo, Gia-Wei Chern The effect of interactions in topological states is a topical issue; not only interaction-enabled topological phases but also novel symmetry-breaking phases and phase transitions are possible. Here we study the effect of interactions on Majorana zero modes (MZMs) bound to a square lattice of vortices in 2D topological superconductors. In the special neutrality condition, where the usual hybridization term for MZMs is prohibited by symmetry, we show that a minimal model for MZMs can be faithfully mapped to a quantum spin model, which has no sign problem in the world-line quantum Monte Carlo simulation. Guided by an insight from a further duality mapping to a compass model, we demonstrate that the interactions induce a Majorana stripe order spontaneously breaking translational and rotational symmetries. Away from the neutrality condition, mean field theory suggests a quantum critical point induced by hybridization, beyond which a Dirac cone appears in the excitation spectrum. |
Wednesday, March 7, 2018 5:06PM - 5:18PM |
P14.00012: Topological cascade lasers for frequency comb generation. Laura Pilozzi, Giulia Marcucci, Claudio Conti Recent progress of topological photonics is enabling their applications in integrated devices. Among these novel light sources, topological lasers, relaying on the special edge states of topological insulators, protected against imperfections and disorder, have been recently proposed. |
Wednesday, March 7, 2018 5:18PM - 5:30PM |
P14.00013: Model of two-dimensional topological insulators with Su-Schrieffer-Heeger electron-lattice coupling Linghua Zhu, Keun Hyuk Ahn We present a model of two-dimensional topological insulators, in which electronic states coupled to lattice distortions through the Su-Schrieffer-Heeger mechanism have non-trivial topological properties. Electronic properties of various twin and antiphase boundaries are calculated for the model and compared with the predictions based on topological arguments. |
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